The present invention generally relates to methods and apparatus for the high rate deposition, synthesis and/or analysis of materials on an array of electrodes, and the desired materials developed from the methods. More specifically, the invention is directed to methods of high rate synthesis and/or analysis of an array of materials wherein deposition control techniques in conjunction with the electrode array are employed to develop a meaningful array of materials and to analyze the materials for a desired characteristic to develop one or more materials with the desired characteristics.
Developing new and useful materials, in the past, has been by prediction of the general chemistry of compositions and applying known testing methods to a small number of synthesized materials. Even with predicting and applying the currently known chemistry of materials, the number of materials that are predicted in a group is too large to properly analyze. The result of only analyzing a few materials in a predicted group leaves the great majority of predicted useful materials unexplored. Thus, the discovery and development of new materials have need for a method of synthesizing and analyzing new materials with a large number of variable compositions at a high throughput rate.
Combinatorial methods represent a new set of experimental tools that are well suited to explore systems comprised of a very large number of variable compositions. As a consequence of this characteristic, there has been a great deal of recent activity in the application of combinatorial synthesis to drug discovery, Chem. Rev. 1997, 97(2), where such large number of variable compositions are commonplace. In cases such as these, a great many different chemical structures need to be examined to find structural motifs, amino acid sequences (e.g. in bioactive polypeptides), or other molecular characteristics that exhibit the desired effect. The key to success in these efforts has been to exploit the power of combinatorial methods both for doing chemical reactions and for examining the efficacy of the resulting compounds, all in a parallel or high-speed serial fashion. The range of types of synthetic schemes and the systems to which they have been applied is typified by the articles in Chemical Reviews theme issue (Chem. Rev. 1997, 97(2)).
More recently, several groups have begun to apply combinatorial methods to materials problems. An example of this trend is the work being done at UC Berkeley by Schultz et al. To date, these groups have focused predominantly on materials properties, especially luminescence. Also, a recent report by Mallouk et al. points to the use of such methods in electrochemical applications (Science, 1998, 280, 1735). Specifically, Mallouk et al. used ink jet processing to deliver multiple metal complexes that served as electrocatalyst precursors to specific sites on a conductive substrate, employed chemical methods to reduce the complexes to produce metallic alloys and then used a novel fluorescence-based method to look for methanol oxidation activity. This appears to be one of the first uses of combinatorial methods in development of electrocatalysts. A particularly useful feature of this method was the demonstration of a parallel testing method. In addition to the efforts described above, several other groups have begun to explore the use of combinatorial methods for synthesis of materials with novel properties (Briceno et al. Science, 1995, 270, 273; Kobayashi et al. J. Am. Chem. Soc. 1996, 118, 8977).
An electrode""s oxidation and reduction capabilities have led to the use of electrodes performing an essential step in synthesizing materials. One of the earliest description of using electrodes in combinatorial synthesis is by Fodor et al. (U.S. Pat. No. 5,424,186). Microelectrodes are used to remove protecting groups in the synthesis of organic molecules. Fodor et al. position an electrode over the protecting group to activate the desired deprotection step. Because of an electrode""s versatility and control, the use of an array of electrodes in synthesis and analysis of materials is forthcoming.
In depositing materials onto an electrode many factors contribute to the composition of the material in the array. Some factors even affect the deposited materials in a solution after the material has already been deposited and other compositions are being deposited. In WO98/03521, Weinberg et al. express the need for homogeneous compositions of materials for a meaningful analysis of an array of materials. However, little work has been done to ensure that the array of materials may be analyzed for a desired characteristic and not for unwanted variations in morphology or composition.
An important feature of combinatorial synthesis is the ability to deposit meaningful compositions at discrete electrodes at a high rate of speed. In PCT WO98/14641, the complete disclosure of which is incorporated herein by reference for all purposes, McFarland et al. show an array of electrodes used for combinatorial synthesis and analysis, however, the use of changing out or adding components of the solutions in a solution bath results in an increased number of solutions when a hundred compositions are synthesized. Additionally, when more electrodes are employed to synthesize thousands or ten of thousands of compositions, the number of solutions or additions to solutions needed adversely affects the ability of high-throughput synthesis of compositions. McFarland et al., in WO98/14641, attempt to alleviate the need for a high number of solutions or additions to solution by using a variety of potentials at different electrodes to attempt to adjust the deposition of certain components in the solutions to vary the compositions at the electrodes electronically. While this method may result in a desired library of compositions, the compositions are affected by the method used to deposit and any meaningful analysis or screening is adversely affected by the morphology of the compositions. McFarland et al. discuss how multiple samples of varying composition can be prepared from solutions carrying various metal salts. However, they do not take the necessary steps to produce controllable morphology during the deposition or to maintain the composition of the samples after the deposition. For instance, when electrodepositing metals from solution at overpotentials that vary, a wide variety of surface morphologies are created. Those surface morphologies preclude easy and rapid comparison of the physical or chemical properties of the samples, specifically of the electrochemical, catalytic, or optical properties. Furthermore, when electroplating from solutions that contain Ni, Fe, Cu, and Zn, deposited samples that contain Zn, Ni, or Fe at their surfaces, the Zn, Ni, or Fe will react with the solution-bound salt of Cu to dissolve Zn, Ni, or Fe and deposit Cu. Similar reactions occur between Zn and Ni and between Zn and Fe. This general type of reaction occurs between any two species where the redox state of one species is at a less positive potential than the redox species of another species in the same environment. These reactions inadvertently change the surface compositions and morphologies of the deposits that have been prepared but remain in contact with the precursor-containing solution. Thus, controllable high-throughput synthesis and analysis of new materials using an array of electrodes is not yet feasible.
In order to synthesize and analyze a large number of new materials, a method of developing and analyzing new materials on an array of electrodes employing control techniques to ensure desired compositions and morphologies at known locations on the array is desirable.
The present invention provides methods and apparatus for the high rate deposition, synthesis and/ or analysis of materials of various compositions onto an array of electrodes, and the materials developed from the methods. In particular, the present invention provides methods of high rate synthesis and/or analysis of an array of materials wherein deposition control techniques in conjunction with the electrode array are employed to develop a meaningful array of materials wherein the array of materials may be analyzed for desired characteristics to develop one or more materials with the desired characteristics.
In order to synthesize a large number of materials with varying compositions, an array of electrodes is employed. The array allows the control necessary for high-throughput synthesis of new materials. The array uses a conducting material to contact two or more discrete conducting regions to produce two or more electronically-discrete electrodes. The array has two or more electronically-discrete electrodes which are addressable individually or collectively, in serial or in parallel, using electronic, optical, or mechanical means, via passive or active, internal or external circuitry. The use of the array of electrodes is preferably by addressing the discrete electrodes individually AND collectively. The electrodes provide an electrical potential or electrical current to initiate deposition of a desired composition at the electrode. The electrodes are controlled by means that allow a predetermined composition to be deposited at a known electrode. Thus, for any given electrode the composition of the material deposited at that electrode is known when the entire array of materials has been synthesized. The electrode array consists of two or more electronically-discrete electrodes, preferably of twenty or more electronically-discrete electrodes, or, more preferably, of 100 or more electronically-discrete electrodes, or, more preferably, of 1000 or more electronically-discrete electrodes, or, more preferably, of 10,000 or more electronically-discrete electrodes, or, most preferably, of 100,000 or more electronically-discrete electrodes.
The deposition of materials onto the array of electrodes may be by electrodeposition or co-electrodeposition of one of more elements via reductive or oxidative passage of one or more electrons between the electrodes comprising the array or from some external electrode assembly and the elements, assembly of elements, or chemical or physical assemblies containing the element or elements; electrophoretic deposition of one or more elements via electrostatic interaction between the elements, assembly of elements, or chemical or physical assemblies containing the element or elements and the electrodes comprising the array or from some external electrode assembly; electrochemically-, chemically-, or physically-induced deposition or precipitation of elements, assembly of elements, or chemical or physical assemblies containing the element or elements; or spontaneous precipitation of elements, assembly of elements, or chemical or physical assemblies containing the element or elements.
Deposition may include the introduction of the electrode array into a solution or mixture of components for deposition. Alternatively, the solution or mixture may be introduced to the electrode array. The solution or mixture entrains the components for deposition and supplies the components for deposition onto the electrode when the electrode is addressed in some fashion. The variation of the deposition components in the solution or mixture is controlled to allow a known composition to be deposited at a known electrode. The controlled variation of the deposition components may be achieved by any method wherein the known deposition components are present at the known electrode to deposit the known composition at the electrode.
Deposition may also employ the use of a counter-electrode and reference electrode or simply a counter electrode. The counter-electrode provides current to complete the circuit through the cell. The reference electrode provides for control of the potential applied at the electrode in the array of electrodes.
In order to ensure that the array of materials may be meaningfully analyzed, various deposition control techniques are employed. The deposition of materials onto an array of electrodes may lead to varying morphologies amongst the varying materials on the array. One discrete material deposited at one discrete electrode may have an extremely rough surface or morphology compared with the other materials deposited at other electrodes. With some deposition techniques, the morphologies may vary material to material. When analyzing the materials, some desired characteristics are affected by the morphology, and the ability to control morphologies along with other deposition characteristics is highly critical to the analysis of the materials for desired characteristics.
Alternately, the ability to deliberately generate a wide variety of morphologies is highly desirable when such morphologies comprise desired characteristics of the deposits.
The control techniques include methods to adjust or control the morphologies of the depositing or deposited materials, methods to protect the deposited materials from further reactions, methods to control the potential at the electrodes where deposition has occurred, methods to control the exchange of reactive species at deposited materials, methods to control the potential at the depositing material methods to cap or passivate the deposited material, methods to control the current at the electrodes, methods to control the counter-electrode or reference position and other methods to deposit a homogeneous material at discrete electrodes. The control techniques and methods are not limited to the deposition process and may include methods to control or adjust the materials after deposition of all materials on the array. These methods may include additional steps before analysis wherein the materials are processed further to ensure a homogeneous composition at each electrode or one or more homogeneous characteristic at each discrete composition location that is suitable for analysis of the desired characteristic sought.
The methods employed to control the deposition of the materials onto the electrode array include but are not limited to pulse electrodeposition, potential control to avoid exchange reactions, overpotential electrodeposition, the use of kinetically sluggish precursors, the positioning of one or more counter-electrodes or reference electrodes and the use of passivating layers.
After deposition of the materials on the electrode array an additional step may be employed to further process the materials for analysis. The processing step may occur while the material array is still within contact of the solutions or other components of the deposition step. Processing may include exposure of the array of materials to gaseous, liquid, or solid reactants, controlled heating or cooling of the array of materials, and treatment of the array of materials with electromagnetic radiation of wavelength between 10xe2x88x9216 m and 10xe2x88x9218 m.
This invention also relates the use of arrays of electrodes as described to analyze materials comprising two or more elements. The array of electrodes may be used to synthesize the array of materials, but the array need not be used to synthesize the materials. Preferably, the array of electrodes is used to synthesize and analyze the array of materials. Methods used to analyze the array of materials may or may not comprise combinations of one or more methods including, but not limited to electrochemical analysis of materials via the electrodes contained in the array or via some external electrode assembly. Other analysis techniques include electrochemical analysis of the materials using electrochemical methods including but not limited to potentiometry, coulometry, voltammetry, and polarography; analysis of the materials via optical methods including but not limited to infrared, Raman, electronic absorption, fluorescence, phosphorescence, and chemiluminescence spectroscopies, atomic spectroscopy, emission spectroscopy based on plasma, arc, and spark atomization, nephelometry, turbidity, refractometry, polarimetry, rotatory dispersion, and circular dichroism; analysis of the materials via x-ray spectroscopies including, but not limited to, x-ray fluorescence, absorption and diffraction spectroscopies; analysis of the materials via electron spectroscopic methods including, but not limited to, x-ray photoelectron spectroscopy, ultraviolet photoelectric spectroscopy, Auger spectroscopy, ion neutralization spectroscopy, electron impact spectroscopy, and penning ionization spectroscopy; analysis of the materials via nuclear magnetic resonance methods including, but not limited to, nuclear magnetic resonance spectroscopy and electron spin resonance spectroscopy; and analysis of the materials via other methods including, but not limited to, radiochemical methods, mass spectrometry, conductometric methods, thermal methods, and chromatographic separations.